I have been looking at a few jobs for a for a loft conversion company as they need a sparky. 1 lighting circuit, 1 ring circuit and 1 circuit for mains smokes are installed in to the loft area. There has been 6 way rewirable units in the houses and usually the fuses have been doubled up and even three circuits feed from one fuse. I have been advised them to change the consumer unit to a new 10/12 way mcb board etc. they are saying no, just put a 3/5 way supplementary unit in off of a henly block. and leave the existing unit as is due to cost. dont like the idea myself. any advise?

the tails would come from the meter to the henly block then to the main house cu with a main 2 pole isolater, and to the loft supplementary cu with a main 2 pole switch. both protected by main supply company fuse head.

I suppose you have to remember is the builder will have put a price in for the electrics and the less he can get you to do the more money he makes, I think its time for 'take it or leave it'.

regards

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"Take nothing but a picture,leave nothing but footprints!"-------------------------"Oh! The drama of it all."-------------------------"You can throw all the philosophy you like at the problem, but at the end of the day it's just basic electrical theory!"-------------------------

What exactly is wrong with the practice the builder is suggesting? Have you ever read Brian Scaddans electrical installations publication? In his example of installing a 9KW kiln, he advocates that exact practice. Personally I try never to do this, but I have been advised to do it several times by the NICEIC.

I never said any such thing. Read my post again.
The publication I speak of is well known and I believe that Mr Scaddan is an honary member of the city & guilds and examiner.
I have pointed out that he has advocated this practice in his book. Therefore I'm asking the question, how is it that he recommends such a practice if it is wrong?

Unless there's an switch-disonnector (isolator) before the henleys, you'd not have a single main switch for the installation - 460-01-02.

Reading 460-01-02.....

It also states that where and installation is supplied from more than one source, a main switch shall be provided for each source of supply and a durable warning notice shall be permanently fixed in such a position that any person seeking to operate any of these main switches will be warned of the need to operate all such switches to achieve isolation of the installation.

Could you call 2 CCU's fed from a common henley block to be 2 sources of supply to an installation? Is so then could you get away with suitable warning notices?

Interesting banter here.
Ok radial (lighting circuit say) loop in to 1st rose, from first rose loop out in opposite directions to another two (seperate radials) then from these two each to another two ad infinitum. Well up to circuit maximum for current draw.
A tree (or branch or bush or nightmare to PIR anyway LOL ) but wrong or non complying?
The same circuit with umpteen radials fed from the same fuseway on a board then, does it comply or is it as safe/less safe to a greater or lesser extent?
OK more difficult to I & T but that does not make it right to condem out of hand as many would do IMHO (as well as the I & T you`d actually have to do calcs rather than rely on conventional circuit arrangements as defined in the OSG. Remembering that such not listed as conventional circuits may still be correct to BS 7671 but if you defect them you might actually be sued by the original designer/installer).
Well that`s my take on it.
In brief, unconventional does not always equal incorrect

Reminds me slightly of the wrong circuit thread I did recently in that I might not like it at all but difficult to realistically condem. Gosh though, if life was so simple the we`d all live it easily and learn nowt from others

Ok radial (lighting circuit say) loop in to 1st rose, from first rose loop out in opposite directions to another two (seperate radials) then from these two each to another two ad infinitum. Well up to circuit maximum for current draw.

A tree (or branch or bush or nightmare to PIR anyway LOL ) but wrong or non complying?

The same circuit with umpteen radials fed from the same fuseway on a board then, does it comply or is it as safe/less safe to a greater or lesser extent?

OK more difficult to I & T but that does not make it right to condem out of hand as many would do IMHO (as well as the I & T you`d actually have to do calcs rather than rely on conventional circuit arrangements as defined in the OSG. Remembering that such not listed as conventional circuits may still be correct to BS 7671 but if you defect them you might actually be sued by the original designer/installer).

Well that`s my take on it.

In brief, unconventional does not always equal incorrect

Reminds me slightly of the wrong circuit thread I did recently in that I might not like it at all but difficult to realistically condem. Gosh though, if life was so simple the we`d all live it easily and learn nowt from others

Going back to the first question about 6way rewirable board, having multi circuits from each fuse, don't reg 314-01-04 cover this ?.

Nope, because the definition of a circuit (see part 2) is anything "protected against overcurrent by the same protective device" - so everything connected to one fuse is therefore the same single circuit - regardless of how many cables there are. (I think you'd have to connect a circuit (e.g. each log of the same ring) to two different fuses or borrow a neutral to contravene 314-01-04).

andy
it may be the way we both interpret the regs i see each cable coming out of a fuse as a final circuit.
that why it comes under installation of circuit arrangment.
having say 3 or 4 lighting circuits coming out of one fuse which wont blow because its not over load not make it right.

it may be the way we both interpret the regs i see each cable coming out of a fuse as a final circuit.

that why it comes under installation of circuit arrangment.

having say 3 or 4 lighting circuits coming out of one fuse which wont blow because its not over load not make it right.

den

now i may be wrong

Yes you are - wrong that is

We have ring circuits and radial circuits. Some countries have tree circuits - one trunk and then a number of branches.

We are discussing a circuit that consists of a number of radial runs from a CPD - so what will we call it? - A brush circuit, or may be a bush circuit, or you decide - answers on a postcard please.

Remember we can have rings with a spur from the CPD and we could of course have multiple trees from the same CPD .

The point is, as others have pointed out above, we can have anything we like provided it complies with BS 7671 and that means that it has: over current protection, shock protection etc, etc. BS 7671 wisely does not specify the precise format of the circuit (the IEE stopped doing that when the 15th edition came out).

You may call these things bad practice but I recommend that you think carefully about that - what is it that makes them bad?.

Exactly. I still agree with Andy's definition of a circuit from earlier though. What is important, and that goes for any termination, is that the number and size of conductors joined should not exceed the manufacturer's recommendations.

Originally posted by: tony30off topic slightly but with a domestic, 24 hour, off peak and bottom immersionsupply this = 4 tails how do you isolate them, remember theres a neutral too.

5 live conductor!!!

With Economy 7 (or equivalent), we often see a four-pole main switch - often two 2-pole switches with a linking bar on the operating handle. How about three 2-pole switches linked, although you would have to put it in a small consumer unit housing!

The four-pole arrangements are often for flats with a common meter room, and are accomodated in a small consumer unit at the meter position, with two mcbs to protect the extended meter tails (normal & E7).

To answer the original Q:
IMO, a warning notice that there is more than one main switch for isolation makes the installation comply.
Not the best practise, agreed, but I can't see where a code 2 comes from.